The reduction of 4-nitrobenzene diazonium electrografted layer: An electrochemical study coupled to in situ sum-frequency generation spectroscopy
The reduction of 4-nitrobenzene diazonium electrografted layer: An electrochemical study coupled to in situ sum-frequency generation spectroscopy
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DOI：
10.1016/j.electacta.2018.07.073
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发表时间：
2018-09
影响因子：
6.6
通讯作者：
W. Richard;David Evrard;B. Busson;C. Humbert;L. Dalstein;A. Tadjeddine;P. Gros
中科院分区：
文献类型：
--
作者：
W. Richard;David Evrard;B. Busson;C. Humbert;L. Dalstein;A. Tadjeddine;P. Gros
本文报道了4-硝基重氮苯（4-NBD）在玻碳（GC）电极上的电化学还原-原位和频发生（SFG）技术。4-NBD在0.3 V（饱和甘汞电极（SCE））下接枝到GC上后，SFG允许在1349 cm− 1或1353 cm− 1处观察到归属于硝基（NO2）基团对称振动模式的清晰信号，这取决于光谱是在空气中还是在溶液中记录的。该结果证明，4-NBD接枝实际上在高达0.3V vs. SCE的电势下发生。结合SFG数据和循环伏安法（CV）也表明，在此电位下，NO2基团没有发生还原成羟胺（NHOH）或胺（NH 2）的过程.在-0.1 V下电解接枝的NO2部分，然后进行CV和原位SFG。NO2信号的指数衰减位于1353 cm−1vs。电解时间与固定在电极表面的物质的电荷转移限制反应速率一致，并且允许NO2还原的一级动力学速率常数被估计为k = 0.006s-1。在相应的循环伏安图（CV）上观察到的归因于NO/NHOH可逆体系的峰的积分表明，NO2还原产生羟胺和胺基团，并且不是定量的。SFG光谱是沉默的长电解时间值的事实表明，剩余的硝基位于远离电极表面，作为一个结果的电子隧穿效率降低整个膜厚度。在-0.8 V下进一步电解，剩余的硝基被还原成NH 2，几乎可以定量。所有这些结果表明，在电解过程中存在分层层，其中没有由于H+在有机膜中的扩散的限制。
This work describes an electrochemical study of 4-nitrobenzene diazonium (4-NBD) reduction onto glassy carbon (GC) electrode coupled to in situ sum-frequency generation (SFG) spectroscopy. After 4-NBD grafting at 0.3 V vs. saturated calomel electrode (SCE) onto GC, SFG allowed a clear signal assigned to the symmetrical vibration mode of the nitro (NO2) groups to be observed at 1349 cm−1or 1353 cm−1depending on whether the spectrum was recorded in air or inside the solution. This result proved that 4-NBD grafting actually occurs at a potential as high as 0.3 V vs. SCE. The combination of SFG data and cyclic voltammetry (CV) also indicated that at such a potential, NO2groups did not experience reduction process into hydroxylamine (NHOH) or amine (NH2) groups. The electrolysis of grafted NO2moieties at −0.1 V was followed by CV and in situ by SFG. The exponential decay of the NO2signal located at 1353 cm−1vs. electrolysis time was in accordance with a charge transfer-limited reaction rate for a species immobilized at the electrode surface, and allowed a first order kinetic rate constant for NO2reduction to be estimated k = 0.006 s−1. The integration of the peaks observed on the corresponding cyclic voltammograms (CVs) which were attributed to the NO/NHOH reversible system showed that the NO2reduction produced both hydroxylamine and amine groups and was not quantitative. The fact that SFG spectroscopy was silent for long electrolysis time values suggested the remaining nitro groups to be located far from the electrode surface, as a consequence of an electron tunneling efficiency which decreased throughout the film thickness. Further electrolysis at −0.8 V allowed the remaining nitro groups to be reduced into NH2with almost quantitative yields. All these results suggest the existence of a stratified layer during the electrolysis process, in which there is no limitation due to H+diffusion in the organic film.